The present invention relates to a colored thermoplastic resin composition containing a black dye exhibiting excellent dispersibility and/or compatibility for a crystalline thermoplastic resin, a method for molding said colored thermoplastic resin composition, a method for lowering the crystallizing temperature of a thermoplastic resin, and a fiber-reinforced colored thermoplastic resin molded product.
Being excellent in mechanical and chemical properties, thermoplastic resins are widely used for molded plastic products in the field of parts of automobiles, electric and electronic products, etc., and their demand is increasing in the field of engineering plastics as well.
As such, thermoplastic resins are colored for decoration, color identification, improvement of light fastness of molded products, content protection and shading and for other purposes; in particular, black coloring is the most important for industrial applications. Traditionally, various inorganic pigments and organic dyes/pigments, such as carbon black, black metal complex dyes, azine dyes and perinone black, have been used for black coloring of thermoplastic resins.
More specifically, examples of colored thermoplastic resins include a molding formula comprising a polyamide resin colored with carbon black and nigrosine (Japanese Patent Examined Publication no.43379/1985); a molding composition comprising a polyamide resin colored with carbon black and a copper phthalocyanine pigment (Japanese Patent Unexamined Publication No. 226551/1985); a molding composition comprising an unsaturated polyester resin colored with aniline black and solvent blue (Japanese Patent Examined Publication No. 46524/1989); a plastic molding composition comprising a thermoplastic resin supplemented with carbon black and titanium oxide (Japanese Patent Unexamined Publication No. 186633/1993); a colored resin composition comprising a thermoplastic resin colored with a red organic pigment, a blue organic pigment and a yellow organic pigment (Japanese Patent Unexamined Publication No.230278/1993); and a mixed resin of polyethylene terephthalate resin and polybutylene terephthalate resin with carbon black dispersed therein (Japanese Patent Unexamined Publication No. 194825/1993).
However, these conventional colored thermoplastic resin compositions do not always have good appearance and surface gloss, many of which undergo physical property deterioration in comparison with the original thermoplastic resins; further investigation remains to be conducted.
In addition, there have been attempts to improve the heat resistance and chemical resistance of thermoplastic resins and confer mechanical characteristics suited for various uses, by formulating a fibrous reinforcing material therein, to meet the requirements of a wide variety of industrial applications. Furthermore, in recent years, there has been a marked trend toward replacement of conventional metal parts of electronic products, electrical equipment for automobiles, etc. with fiber-reinforced thermoplastic resins, for the purpose of weight reduction, manufacturing process simplification and corrosion prevention, taking note of the good physical properties of fiber-reinforced crystalline thermoplastic resins as molding materials.
Examples of conventional fiber-reinforced colored thermoplastic resins include a polyester resin composition for molding comprising a polybutylene terephthalate having a specific viscosity of not less than 0.35, a reinforcing material and carbon black (Japanese Patent Unexamined Publication No. 117951/1990); a thermoplastic resin composition comprising a thermoplastic resin, a modified polyolefin, a fibrous reinforcing material and carbon black (Japanese Patent Unexamined Publication No. 50263/1991); a glass fiber-reinforced black polyamide resin composition comprising a polyamide resin, surface-treated glass fiber and an azine dye (Japanese Patent Unexamined Publication No. 128479/1994); and an antistatic-fiber-reinforced polybutylene terephthalate resin composition comprising a glass fiber-reinforced polybutylene terephthalate resin having a volume resistivity of not more than 1xc3x971010 xcexa9cm, and carbon black formulated therein (Japanese Patent Unexamined Publication No. 53610/1996).
In conventional fiber-reinforced colored thermoplastic resins, however, the problem is likely to arise in which it is difficult to thoroughly and uniformly disperse a coloring agent (e.g., black pigment) in the resin even by kneading them together for a long time, because of the presence of a fibrous reinforcing material in the resin. In addition, adding a coloring agent can deteriorate the physical properties, can intensify the warpage deformation of the molded product due to a temperature change during molding, or can considerably reduce the fluidity, in comparison with the original thermoplastic resin which does not contain the coloring agent. In particular, the flotation of the fibrous reinforcing material on the surface of the molded product during molding is somewhat problematic in that the gloss, appearance, etc. of the colored molded product are affected.
For these reasons, there is a strong commercial demand for a fiber-reinforced colored thermoplastic resin which is moldable at high precision for details, which has good light fastness, and which exhibits better gloss and appearance in the markets of various molded products etc.
In addition, injection molding, a method for molding a thermoplastic resin, is a method wherein a plastic material, previously fluidized by heating, is injected into the hollow (cavity) of a mold and cooled and solidified in the mold to yield a molded product fitting to the inside shape of the cavity, making it possible to obtain products of high precision and high quality with highest efficiency and productivity.
In this case, the temperature of the mold governs the cooling solidification conditions for the molten resin filled in the mold. Specifically, as the difference from the resin temperature increases (mold temperature decreases), the cooling rate increases. In the case of a crystalline material, in particular, there is a remarkably high correlation between cooling rate and degree of crystallinity, and the degree of crystallinity significantly affects the physical property values of the molded product.
Regarding the general tendency, as the mold temperature decreases, the degree of crystallinity decreases and the molded product becomes more ductile. As the mold temperature increases, the degree of crystallinity increases and the strength of the molded product becomes higher but the molded product becomes more brittle.
Injection time in injection molding refers to the period of time during which a thermoplastic resin is inject-filled in the cavity. In the case of a thin molded product, injection time shortens. As the molded product becomes larger, more complex, and thicker, more injection time is taken. It is therefore possible to mold a more complex molded product by broadening the range of optimum injection time for a thermoplastic resin.
In molding treatment of a thermoplastic resin, the temperature at which the material is thermally plasticized varies over a wide range from about 180 to 430xc2x0 C., including the temperature of the heating cylinder. In addition, molding temperature, i.e., the temperature required to cool and harden the material, refers to the temperature of the mold, and normally ranges from about 120 to 200xc2x0 C. Causes of molding failures in the injection molding process include uneven coloring, sinks, short shots, and burned marks. These are caused by high mold temperatures and uneven cooling circuits. The flow mark is known to be a molding failure and to be prevented by increasing the mold temperature. If the mold temperature is increased, however, additional heat energy is required; in addition, a great amount of heat energy must be transferred to cool the once-heated mold; these factors raise production cost. Furthermore, if the mold temperature is increased, a greater amount of gas is generated; the surface of the molded product becomes likely to have clouding (haze) due to gas adhesion, which in turn makes it difficult to obtain a molded product of high gloss.
The present invention was developed in view of the above problems in the prior art. Accordingly, the object of the invention is to provide a colored thermoplastic resin composition which can be molded at low mold temperatures, which is capable of producing a fiber-reinforced or non-fiber-reinforced molded product with improved surface gloss, which has been colored vividly without affecting the characteristics of the original thermoplastic resin, which is good in appearance, surface shape and light fastness, and a method for molding said colored thermoplastic resin composition, a method for lowering the crystallizing temperature of a thermoplastic resin, and a fiber-reinforced colored thermoplastic resin molded product.
(1) The colored thermoplastic resin composition of the present invention for accomplishing the above object is a colored thermoplastic resin composition comprising a crystalline thermoplastic resin containing a black dye, wherein said black dye is a black dye obtainable by a reaction of one or more anionic surfactants selected from the group consisting of (a) to (d) below and nigrosine, and wherein the crystallizing temperature is lower than that of the original thermoplastic resin containing no black dye.
(a) a sulfuric acid ester surfactant
(b) a phosphoric acid ester surfactant
(c) a sulfonic acid surfactant
(d) a carboxylic acid surfactant
Accordingly, the present inventors found that when a black dye obtainable by a reaction of one or more anionic surfactants selected from the group consisting of (a) a sulfuric acid ester surfactant, (b) a phosphoric acid ester surfactant, (c) a sulfonic acid surfactant and (d) a carboxylic acid surfactant, and nigrosine, is formulated in a crystalline thermoplastic resin to color the thermoplastic resin, the dispersibility and/or compatibility of the black dye for the thermoplastic resin is excellent, the black dye in the thermoplastic resin undergoes almost no fading or discoloration during blending, kneading and molding, a uniformly and vividly colored molded product with good surface gloss is obtained, and molding treatment can be smoothly carried out without affecting the fluidity of the thermoplastic resin; and that the light fastness of the molded product is good, the mechanical properties of the molded product are good and are hardly deteriorated by coloring, it is possible to lower the crystallizing temperature of a crystalline thermoplastic resin so that the mold temperature during molding can be set at a low level, the cost for heating the mold and the cost for cooling the mold if necessary are lowered, and a molded product of excellent appearance and high surface gloss is obtained. The present inventors developed the present invention based on this finding.
(1-1) The aforementioned sulfuric acid ester surfactant may be one or more surfactants selected from the group consisting of
an alkyl sulfuric acid ester or a salt thereof,
an alkyl ether sulfuric acid ester or a salt thereof,
a polyoxyethylene ether sulfuric acid ester or a salt thereof,
a polyoxyethylene alkyl ether sulfuric acid ester or a salt thereof,
a polyoxyethylene aryl ether sulfuric acid ester or a salt thereof, and
an alkylamide sulfuric acid ester or a salt thereof.
(1-2) The aforementioned phosphoric acid ester surfactant may be one or more surfactants selected from the group consisting of
an alkyl phosphoric acid ester or a salt thereof,
a polyoxyethylene ether phosphoric acid ester or a salt thereof,
a polyoxyethylene alkyl ether phosphoric acid ester or a salt thereof, and
a polyoxyethylene aryl ether phosphoric acid ester or a salt thereof.
(1-3) The aforementioned sulfonic acid surfactant may be one or more surfactants selected from the group consisting of
an alkylbenzenesulfonic acid or a salt thereof,
an alkylnaphthalenesulfonic acid or a salt thereof,
a naphthalenesulfonic acid salt-formalin polycondensation product,
a sulfosuccinic acid or a salt thereof,
xcex1-olefinsulfonic acid or a salt thereof, and
N-acylsulfonic acid or a salt thereof.
(1-4) The aforementioned carboxylic acid surfactant may be one or more surfactants selected from the group consisting of
a polyoxyethylene ether carboxylic acid or a salt thereof,
a polyoxyethylene alkyl ether carboxylic acid or a salt thereof,
an N-acylamino acid or a salt thereof,
a naphthenic acid or a salt thereof,
an aliphatic amine and aliphatic amide fatty acid or a salt thereof,
an aliphatic amine and aliphatic amide aromatic carboxylic acid or a salt thereof, and
a polycarboxylic acid type high molecular compound or a salt thereof.
(1-5) The colored thermoplastic resin composition of (1), (1-1), (1-2), (1-3) or (1-4)may be one wherein said black dye is contained at 0.1 to 10% by weight per 100% by weight of the thermoplastic resin.
(1-6) The colored thermoplastic resin composition of (1), (1-1), (1-2), (1-3), (1-4) or (1-5) may have a crystallizing temperature lower by not less than 5xc2x0 C. than that of a thermoplastic resin composition containing nigrosine instead of said black dye.
(1-7) The colored thermoplastic resin composition of (1), (1-1), (1-2), (1-3), (1-4) or (1-5) may have a crystallizing temperature lower by not less than 10xc2x0 C. than that of the original thermoplastic resin composition not containing said black dye.
(1-8) The colored thermoplastic resin composition of(1), (1-1), (1-2), (1-3), (1-4) or (1-5) may have a crystallizing temperature lower by not less than 15xc2x0 C. than that of the original thermoplastic resin composition not containing said black dye.
(1-9) The colored thermoplastic resin composition of (1), (1-1), (1-2), (1-3), (1-4) or (1-5), (1-6), (1-7) or (1-8) is preferably one wherein said crystalline thermoplastic resin is polyamide resin, polybutylene terephthalate resin or polyphenylene sulfide resin.
(1-10) The colored thermoplastic resin composition of (1), (1-1), (1-2), (1-3), (1-4), (1-5), (1-6), (1-7), (1-8) or (1-9) is preferably one containing a fibrous reinforcing material.
(2) The method of the present invention for lowering the crystallizing temperature of a thermoplastic resin is a method for lowering the crystallizing temperature, in comparison with the original thermoplastic resin containing no black dye, by containing a black dye in a crystalline thermoplastic resin, wherein said black dye is a black dye obtainable by a reaction of one or more anionic surfactants selected from the group consisting of (a) to (d) below and nigrosine.
(a) a sulfuric acid ester surfactant
(b) a phosphoric acid ester surfactant
(c) a sulfonic acid surfactant
(d) a carboxylic acid surfactant
(3) The method of the present invention for molding a colored thermoplastic resin composition comprises injection-molding the colored thermoplastic resin composition of(1), (1-1), (1-2), (1-3), (1-4), (1-5), (1-6), (1-7), (1-8), (1-9) or (1-10) at mold temperature of 50 to 120xc2x0 C.
(4) The fiber-reinforced colored thermoplastic resin molded product of the present invention is a fiber-reinforced colored thermoplastic resin molded product comprising a crystalline thermoplastic resin containing a fibrous reinforcing material and a black dye, wherein said black dye is a black dye obtainable by a reaction of one or more anionic surfactants selected from the group consisting of (a) to (d) below and nigrosine, and whose surface glossiness is higher than that of a fiber-reinforced colored thermoplastic resin molded product containing nigrosine instead of said black dye.
(a) a sulfuric acid ester surfactant
(b) a phosphoric acid ester surfactant
(c) a sulfonic acid surfactant
(d) a carboxylic acid surfactant
The black dye in the present invention surpasses nigrosine and black pigments, which have traditionally been used for coloring thermoplastic resins, in terms of dispersibility and/or compatibility for crystalline thermoplastic resins. With this feature, the black dye of the present invention is capable of more uniformly black coloring a crystalline thermoplastic resin even when the dry color method is used. This uniform coloring effect is particularly remarkable in a colored thermoplastic resin composition containing a fibrous reinforcing material, in which coloring agents are unlikely to become dispersed due to the influence of the fibrous reinforcing material.
The colored thermoplastic resin composition of the present invention is stable and unlikely to undergo fading and discoloration even in the heating processes such as extrusion, pellet drying before molding, and molding, and is capable of forming a uniformly colored molded product. In addition, the colored thermoplastic resin composition of the present invention is also suited for a molded product requiring high light fastness, such as a molded product to be kept outdoors or elsewhere.
The colored thermoplastic resin composition of the present invention, which possesses crystallinity, has its crystallizing temperature lowered (by not less than 10xc2x0 C., for example), in comparison with the original thermoplastic resin not containing said black dye, by containing the black dye described above. Crystallizing temperature reduction is particularly remarkable in polyamide resin. On the basis of this crystallizing temperature reduction, the molding temperature for the resin composition of the present invention can be set at a low level. For this reason, it is easily possible to reduce molding cost and suppress molding failures. In addition, because the shrinkage of the molded product upon cooling during molding is decreased, molding precision improves so that the anisotropy of molded product strength can be well reduced; it is therefore possible to obtain a molded product which is excellent in surface gloss (for further increased surface gloss, the crystallizing temperature reduction is preferably not less than 15xc2x0 C., rather than 10xc2x0 C.), appearance and dimensional stability during heating. Regarding the obtainment of a molded product with excellent surface gloss and appearance, this effect is remarkable in the case of a colored thermoplastic resin composition containing a fibrous reinforcing material, which tends to have the fibrous reinforcing material floating on the surface of the molded product.
In addition, the colored thermoplastic resin composition of the present invention, which possesses crystallinity, has a crystallizing temperature lower (by not less than 5xc2x0 C., for example) than that of a crystalline thermoplastic resin composition colored with a black pigment (e.g., carbon black) or conventional nigrosine. For this reason, molding precision is improved and fine ruggedness is unlikely to occur on the surface of the molded product, in comparison with a crystalline thermoplastic resin composition colored with conventional nigrosine or a black pigment such as carbon black, so that a molded product with good appearance and gloss is obtained. This difference is conspicuous in polyamide resin and polybutylene terephthalate resin.
Furthermore, the colored thermoplastic resin composition of the present invention makes it possible to adjust the degree of crystallinity of a crystalline resin composition in a molded product over a desired range, because the allowance for adjustment of mold temperature and injection time in injection molding is broadened as a result of the reduction in crystallizing temperature. By optimally setting mold temperature and injection time, it is possible to improve the surface gloss of a molded product and to suppress its reduction. To obtain a molded product with still better surface gloss, mold temperature can be set at 50xc2x0 C. to 120xc2x0 C., preferably 70xc2x0 C. to 105xc2x0 C., when polyamide resin, for example, is used. As a result, the molded product has the best surface gloss.
Therefore, the colored thermoplastic resin composition of the present invention exhibits the capability of being uniformly colored because the black dye contained as a coloring agent therein is good in dispersibility and solubility in the crystalline resin, and this effect is remarkable in a colored thermoplastic resin composition containing a fibrous reinforcing material. In addition, because the black dye has excellent light fastness, the fading rate is slow and the color hue hardly changes during fading.
Also, many of the additives used to provide various functions for crystalline thermoplastic resins act to raise their crystallizing temperature or lower the surface gloss and appearance of molded products. In contrast, even when such additives are contained, the colored thermoplastic resin composition of the present invention has its crystallizing temperature lowered by the black dye contained as a coloring agent therein, and the gloss and appearance of the molded product are improved.
Because the colored thermoplastic resin composition of the present invention has its crystallizing temperature lowered (by not less than 10xc2x0 C., for example), in comparison with the original thermoplastic resin not containing said black dye as a coloring agent, the temperature of the mold for molding can be lowered. Because the shrinkage of the molded product upon cooling is decreased by conducting molding at a reduced mold temperature, molding precision improves so that the anisotropy of molded product strength can be well reduced and dimensional stability during heating is excellent. For this reason, the composition of the present invention is quite effective in producing a precisely molded product, which undergoes rigorous requirements of dimensional precision. In addition, because the temperature of the mold for molding can be lowered, the cooling solidification time for the molded product can be shortened and the equipment cost for the mold heater can be saved, so that a large molded product can be obtained using relatively small equipment.
In addition, according to the method of the present invention for lowering the crystallizing temperature of a thermoplastic resin, it is possible to lower the crystallizing temperature (not less than 10xc2x0 C., for example), in comparison with the original thermoplastic resin containing no black dye, by containing the black dye in a crystalline thermoplastic resin.
Furthermore, according to the method of the present invention for molding a colored thermoplastic resin composition, because the shrinkage of the molded product upon cooling is decreased, molding precision improves so that the anisotropy of molded product strength is well reduced and dimensional stability during heating is excellent; it is possible to efficiently produce a precisely molded product, which undergoes rigorous requirements of dimensional precision. In addition, the cooling solidification time for the molded product can be shortened and the equipment cost for the mold heater can be saved, so that a large molded product can be obtained using relatively small equipment.
Furthermore, the fiber-reinforced colored thermoplastic resin molded product of the present invention has excellent gloss and appearance and exhibits the capability of being uniformly colored, and because the black dye contained as a coloring agent therein has excellent light fastness, the fading rate is slow and the color hue hardly changes during fading.